1. Field of the Invention
The present invention relates to environmental condition controls. More specifically, the present invention is directed to apparatus for compensating sensor lag in an environmental condition sensor to reduce undershoot and overshoot in an environmental condition control system.
2. Description of the Prior Art
During recovery from an offset environmental condition, e.g., a sensed environmental temperature is different from a desired or setpoint temperature, the temperature of the space being controlled conventionally overshoots the setpoint temperature significantly more than the temperature response of the temperature sensor utilized by a temperature control thermostat. The overshoot effect is a result of the sensor time constant or lag. The amount of deviation between the space temperature and the sensor temperature during a recovery or modification of the temperature to achieve the setpoint level is approximately equal to the sensor slope, i.e., (temperature change).times.(the time constant of the sensor). For example, if the temperature change or ramp rate of the thermostat setpoint is 5.degree. F./hr. then the deviation would be five .times.0.25 hr or 1.25F. Accordingly, if the sensor reading is 71.degree. F. then the actual environmental would be 71+1.25 or 72.25. With a ramp rate of the thermostat of 10.degree. F./hr, the deviation would be 2.5.degree. F. The end result is that to ensure that there will be a minimum amount of overshoot requires that the ramp rate of the thermostat must be limited to approximately 5.degree. F./hr. Accordingly, it would be desirable to provide a compensation circuit for compensating for the deviation of the sensor temperature from the space temperature during a temperature recovery by the thermostat.